The present invention relates to thermoplastic elastomer compositions made from blends of 1-olefin polymers such as polypropylene, styrene-butadiene rubber, and highly saturated elastomers such as highly hydrogenated polybutadiene, polyisobutylene, and other highly saturated elastomers, with the compositions requiring no curing or vulcanization to develop elastomeric properties. Additionally, the invention also relates to partially cured compositions. These partially cured compositions are still thermoplastic and can be repeatedly remolded or extruded and require no further cure.
Heretofore, a few specific types of thermoplastic elastomers have been known. The term "thermoplastic elastomer" has generally been applied to elastomers which can be readily processed and reprocessed, molded, or the like by common or conventional thermoplastic methods and which do not require vulcanization to develop the various physical properties.
Previous specific types of known thermoplastic elastomers are the thermoplastic urethanes, the thermoplastic polyesters, such as the Hytrel brand manufactured by DuPont, and the styrene block copolymers sold under the brand names of Kraton and Solprene, manufactured respectively by Shell Oil Company and Phillips Petroleum.
Another very recent thermoplastic elastomer is a blend of polypropylene and EPDM (ethylene-propylene-nonconjugated diene monomer) as described in U.S. Pat. Nos. 3,758,643; 3,806,558; and 3,862,106 to Fischer of Uniroyal, Inc. The blends are partially cured and contain EPDM in amounts up to 90 percent by weight.
Various prior art patents generally disclose blends of a triblock copolymer such as styrene-butadiene-styrene with a polyolefin such as the following Shell patents, U.S. Pat. Nos. 3,424,649 and 3,793,283. Such patents are not pertinent, however, in that they fail to suggest any blend containing random polybutadiene-co-styrene or any component of a highly saturated elastomer.
U.S. Pat. No. 3,299,174 relates to a blend of polypropylene and a saturated block copolymer as of the S-B-S type.
U.S. Pat. No. 3,830,767 is very similar except that it additionally contains a petroleum hydrocarbon wax to minimize the bleeding of extended oils from the propylene-block copolymer composition. This patent is not pertinent to the present invention in that it also lacks polybutadiene-co-styrene and a saturated elastomer. Still further examples of blends of polypropylene and styrene-butadiene block copolymers include U.S. Pat. Nos. 3,689,595 and 3,850,474 wherein such a blend is utilized for automobile body components. A crosslinked blend is set forth in U.S. Pat. No. Re. 28,688.
Various other prior art patents disclose blends of 1-olefin polymers and elastomers. For example, U.S. Pat. No. 3,572,721 to Harrison relates to a golf ball made from a blend of rubber and a thermoplastic. In order to render the ball effective for use, it must be fully cured.
U.S. Pat. No. 3,665,059 to Mahlman relates to polyphase compositions having, as a continuous phase, a propylene polymer, and as a second phase, a synthetic or natural rubber, which compositions are prepared by disbursing a propylene polymer of substantially submicron particle size in the second phase and by mixing the polymer under conditions which ensure formation of the propylene polymer in a continuous phase.
U.S. Pat. No. 3,701,702 to Schichman relates to a method of free curing rubber by adding polypropylene to synthetic rubbers or to natural rubber, or blends thereof and, thus, lacks any suggestion of saturated elastomers.
U.S. Pat. No. 2,877,206 to Scott relates to a peroxide treatment of blends of polymers of 1-olefins and hydrogenated diene polymers. A cured or vulcanized blend results, which is distinguished from the present invention in failing to suggest a thermoplastic elastomer.
U.S. Pat. No. 4,104,210 to Coran et al relates to blends of 55 to 75 percent by weight of high unsaturated diene rubber with 25 to 45 percent of a polyolefin wherein primarily the toughness, as represented by TS.sup.2 /E where TS is tensile strength and E is Young's Modulus, is increased by at least 50 percent or more than a blend containing 50 percent of each component. Moreover, the rubber particles which have a particle size of 50 microns or less are distributed throughout the polypropylene resin. This patent fails to teach or suggest a triblend, a blend having good to excellent paint adhesion, a blend having a very smooth painted surface, as well as a blend having unexpectedly and significantly improved physical properties at low or very low cure levels.
The above prior art patents, when combined in any combination whatsoever, are still not pertinent to the present invention for at least the reasons that such combination is not rendered obvious by the patents themselves and further in that they relate to different blend compositions which often are fully cured.